Shaft kiln



May 10, 1966 A. H. PACK ETAL SHAFT KILN Filed May 15, 1964 INVENTORS. 4L9E/P7 Ae P4C/f i BY W/ f@ M MP L United States Patent O SHAFT KILN.

Albert H. Pack and William W. Campbell, Ludington,

Mich., assignors to Harbison-Walker Riefraetories Company, Pittsburgh,Pa., a corporation of Pennsylvania Filed May 15, 1964, Ser. No. 367,8473 Claims. (Cl.I 26S-4 9) This application isa continuation-impart of ourcopending application Serial Number 203,659 (now abandoned), filed June19, 1962, having the same title and owned by the same assignee.

This invention relates to shaft kilns and more particularly to verticalshaft kilns useful for. burning such as niagnesite, dolomite, lime andthe like. In vertical shaft kilns, raw material is charged in the top toprogressively pass downwardly through preheating, calcining or sinteringand cooling zones. Air used for combustion and heat transfer isintroduced at the bottom of the kiln and passes countercurrent to thecharge upwardly through the kiln. The kiln is red in any of a variety ofdierent manners. For example, gaseous and liquid fuels are used.

One of the limiting parameters of such a kiln is the uniformity ofthetemperature profile in the burning zone of the kiln. Thiscross-sectional uniformity of temperature is effected by a combinationof operating characteristics including size grading of the charge, thecleanliness and hardness of the charge, uniformity of distribution offuel through the charge, the kind and quality of the fuel used in thekiln, and the operating pressure and temperature thereof.

It is an object of this invention to provide an improved design for avertical shaft kiln which assures a cleaner charge to the burning zone,provides better mixing of the fuel and the combustion air, decreasesundesirable dissociation of carbon dioxide and water vapor, and retardsthe channeling of hot and cold gases. It is another object of thisinvention to provide an improved design for the lining of a shaft kiln,which lining is instrumental in providing a longer campaign life for thekiln, producing a better product with lower fuel consumption, andachieving higher production rates.

Briefly, in a broader aspect, a shaftl kiln lining according to theconcepts of this invention is characterized by a generally ellipticalcross-sectional passage which progressively diverges at space intervalsfrom its top to its bottom to dene a charging zone, a burning zone, agas stream deflection zone, a fuel injection zone, and a cooling zoneopening to the gas inlet.

A better understanding and further features and .advantages of shaftkiln linings, according to -this invention, will become obvious to thoseskilled in the art from a study of the 4following detailed descriptionwith reference to the appended drawings. In these drawings;

FIG. l is a schematic vertical section along the short axis of a kilnlining according to this invention;

FlG. 2 is a schematic vertical section along the long axis of the kilnof FIG. 1; and

FIG. 3 is a top elevation of the kiln of FIGS. 1 and 2.

Before describing the drawings in detail, it should be understood thatthey are merely exemplary of one arrangement, according to the conceptsof this invention, and that the true measure of the spirit and scope ofthe invention is to be as dened by the hereafter set forth claims. i

ln the following description, theA upwardly moving gas stream is tracedto explain its work of preheating, burning and cooling of the downwardlymoving charge.

In FlG. 1, a shaft kiln is shown to include a tubular outer shell 10. Arefractory lining 11 is provided within the outer shell and ischaracterized by an intake 12,

CII

The gas or air intake 18 cornrnuru'cates with a cooling zone 17 ofsubstantially uniform cross section. The cross sectionof the coolingzone and` subsequent interconnected,

zones, described below, is preferably generally elliptical (best seeninFIG. 3). The cooling zone 17 leads to a fuel injection zone 16characterized by inwardly converging walls. The `fuel injection zonesubsequently leads to an inwardly convergingl gas dellection zone15, aninwardly converging burning zone 14, a charging zone 13 of substantiallyuniform, cross section, and the charge intake 12. In practice, a groupof burner ports 19 open through the walls of the zone 16.,

The relative degree of angular convergence between the interconnectedzones is more clearly shownin thevertical section of FIG. 2. In` apreferred embodiment, the walls 17a which denne the cooling zone are ofsubstantially uniform cross section. The walls 16a of the fuel injectionzone are characterized by a slope of about 7 degrecs relative to thevertical; the walls 15a of the gas def llection zone are characterizedby a much sharper slope atapproximately 33 degrees relative to thevertical; the walls 14a of the burning zone are characterized by a moremoderate slope of approximately 11 degrees relative to the vertical; andthe wallsrwhich dene the charging zone 13a do not slope and aresubstantially uniform in cross section.

The vertical section along the short axis, as shown in FIG. 1, does nothave as sharp a delineation between zones, as does the vertical sectionalong the long axis as shown in FIG. 2. However, the interconnectedwalls, which define the sequential gas flow zonesthrough the kiln,always converge or remain vertical and never diverge. The less sharpdelineation 'between zones, when Viewed along the short axis, is theresult of shaping to provide a substantially unobstructed, smoothmerging between the sequential zones.

FIG. 3, which illustrates the progressive converging ellipticalcross-sectional configuration from gas intake to gas outlet, also,illustrates the very sharp convergence or slope of the walls in thegas'deflection zone, as compared to the more moderate convergence orslope in the burning and gas mixing zones.

The unconstricted cooling zone 17 allows the maximum ow of air up thekilnl to recover the heat in' the downwardly moving charge, thus,preheating the air before it is used for combustion of the fuel. Airvelocities in the zone are lower because of the larger cross-sectionalarea, thus, preventing any sweeping out of fines in the charge andcarrying them back up into the burning zone of the kiln to cause lumpingof the charge in that zone. We believe it critical to substantiallyeliminate accumulation of fines in the burning zone since they can causeagglomeration of the load passing through the kiln, thus stopping kilnoperation. The relatively large and unrestricted cooling zone preventscarry back of any fines to the burning zone. In a 20 foot kiln of thetype shown in the drawings, the cooling zone is on the order of 1/3 thevertical height or about 7 feet.

In the fuel injection zone 16, the upwardly moving stream of preheatedair is spatially compressed by the tapering walls, and fuel isintroduced and begins to burn. This zone extends on the order of about1/7 the vertical height of the kiln. In some previous kilns there tendedto be an undesirable temperature gradient vacross the hot zone of thekiln, with a relatively higher temperature in some parts of the chargeas compared to others. These localized higher temperature zones tendedto develop because the hot gases short-circuited or channeled throughthe charge, rather than being evenly distributed across it. Thisresulted in a nonuniformly burned product.

Patented May L0, 196,5.v

However, by the provision of a gas deflection zone above the gas mixingzone, upwardly moving hot gases are directed towards the center of thedownwardly moving charge, to thereby provide substantially uniformheating across the charge before it leaves the burning zone. The gasdeiiection zone extends on the order of -about 1/20 the vertical heightof the kiln. The tapering walls of the burning zone 14 cause theupwardly moving gases to further spatially contract, thus, furtherincreasing their velocity.

The velocity of the gases passing through the charge,

in the hot zones of the shaft kiln, causes the flow of these gases to bein a condition of turbulence. The constantly decreasing cross-sectionalarea of the kiln increases the velocity and also the turbulence,resulting in better mixing of the fuel and preheated air, causing a moreuniform combustion. The very high velocity gradient, caused by the sharptaper in the gas deflection zone 15, results in a short hot zone of veryhigh temperature at the base of the burning zone 14.

The rate of heat transfer between the countercurrently moving charge andgases is a direct function of the degree of 'turbulence of the upwardlymoving gases. The feature of constantly changing cross-sectional areasavailable for gas ow results in a continual increase in the turbulence,resulting in the maximum heat transfer rates.

Further, because of the inherent compression of the burning gases causedby the constricted upper section of the kiln, undesirable .dissociationof carbon dioxide and water vapor to carbon monoxide and hydrogen isretarded, resulting in a shorter hot zone and a lower temperature at thetop of the kiln.

The constricted charging zone 13 assists in assuring a cleaner change tothe burning zone due to a high velocity sweeping effect, which preventsthe accumulation of iines in the descending load. Here again, we believeit critical to prevent accumulation of iines in the descending loadbecause we do not wish build-up of lines in the burning zone. Theconstricted charging zone 13, an just noted, is important in assuringcleaner charge to the burning zone. It is able to accomplish thisbecause of two important characteristics. First, it is relatively short,i.e., less than a quarter of the length of the kiln, as can be seen fromthe drawings which are approximately to scale. This short length isnecessary to prevent the gas stream from cooling too much since suchcooling, with commensurate reduction in volume of gas, wouldundersirably reduce discharge gas velocity. Further, we find that, bymaintaining this short zone 13, the gas velocity is sufficient to blowpractically all line material from the charge.

The hot discharging gas stream, including the lines, is

subsequently subjected to dust removal equipment, such as, a cycloneseparator or the like, to prevent discharge of the very line dustparticles into the atmosphere. Here again the higher velocity andturbulence, than in the u sual straight sided kiln, provide far betterheat transfer and preheating of the charge moving down to the burningzone. In a -foot kiln of the type shown in the drawings, the chargingzone is on the order of 1/5 to 1A@ the vertical height or about 2 to 4feet.

Compared to previous shaped kilns ours is remarkably short in thepreferred embodiment, i.e., on the order of 20 feet. We find thisnecessary to obtain the very high temperatures We desire in the burningzone, i.e., well over 3000 and even 3,500 F. Still further, We iind itimportant that the fuel injection zone be at, at least,-

the midpoint of the kiln, or else we do not accomplish our desired hightemperature operation.y Considering our preferred and exemplary 20-footkiln, dimensions of parts are as follows: The zone 17 is above 7 feet invertical extent. The zone 16, which is about 1/7 the vertical extent ofthe kiln, is on the order 'of 3 feet. Thus, the zones 16 and 17 amountto about 1/2 the vertical extent of the` kiln. Just above midpoint isthe gas deflection zone 15, which is ,about 1/20 the vertical extentofthe 4. v kiln or 1 foot. In our exemplary 20-foot kiln, these threezones amount to about l1 feet of the kiln. Zones 14 and 15 are bothabout the same vertical zone extent, but the charging zone is on theorder of 2 to 4 feet in vertical extent. The remaining, about 5 feet, isthe zone 14.

Another reason for locating the gas deflection Zone 15 at, at least, themidpoint is to assure very high temperature in the zone 14 andparticularly the zone 13, to further assure the gas velocity isparticularly high to blow the fines to the top of the kiln.

The combination of (l) the converging walls of the gas mixing zoneallowing good mixing of the fuel and combustion air, (2) the sharpconvergence of the walls of the gas deflection zone, and (3) thesubsequent, more gentle, convergence of the burning zone resulting in ashort hot zone of uniform temperature, together, provides for a higherkiln throughput with a higher quality product, which has not beenpossible with previous vertical shaft kilns because of undesirable gaschanneling characteristics.

The material selected for fabrication of a lining for a kiln accordingto the concepts of this invention may` be, such as, high puritymagnesite lbrick or ramming mix, chrome ore ramming mix, high purityalumina brick or ramming mix and the like, or combinations of the above.In any event, the material selected will obviously depend on thecomposition of the charge to be burned, the temperature at which theoperation is to be conducted, and 4other operating parameters.

Having thus described the invention in detail and with suliicientparticularity as to enable those skilled in the art to practice it,|what we have desired to have protected j by Letters Patent is set forthin the following claims.

We claim:

1. In a vertical, tubular shaft kiln having a bottom gas intake and atop gas discharge, a tubular outer shell, a refractory lining positionedin said shell, said refractory lining constructed and arranged to definean internal passage, the slope `of the inner face of the lining whichdefines the internal pass-age progressively diverging at spaced pointsfrom adjacent its top to a point intermediate its ends to sequentiallydefine contiguous, interconnected treatment zones in the followingprecise order:

(a) a charging zone of substantially uniform cross section extendingfrom the gas discharge to a point intermedi-ate the ends of the kiln,

(b) a burning zone opening from the bottom of said charging zone andcharacterized by moderately diverging walls,

(c) a gas deflection zone opening from the bottom of said burning zoneand characterized by sharply diverging walls, the degree of wall slopein the gas stream deection zone. being on the order of about three timesas great as the degree of slope of the wall .defining the burning zone,said gas stream deection zone being located at about the midpoint of thevertical extent of the refractory lining in said shell, said gasdeflection zone causing the preheated air and fuel gases to be divertedtoward the center of the internal passage,

(d) a fuel injection zone' opening from the bottom of said gasdeflection zone and characterized by moderately diverging walls, thedegree of slope of the wall which defines the fuel injection zone beingon the order of about one fourth the slope of the wall which defines thegas stream deflection zone, Y

and (e) a cooling Zone of substantially uniform cross section openingfrom the bottom of said fuel injection Zone and terminating at the gasintake at the botl tom of said kiln. 2. In a vertical, tubular shaftkiln having a bottom gas intake and a top gas discharge, a tubular outershell, a refractory lining positioned in said shell, said refractorylining constructed and arranged to deiine an internal passage, the slopeof the inner face of the lining which defines the internal passagesprogressively diverging at spaced points frorn adjacent its top to apoint intermediate its ends to sequentially define Contiguous,interconnected `treatment zones in the following precise order:

(a) a charging zone of substantially uniform cross section extendingfrom the gas discharge to a point intermediate the ends of the kiln,

(b) a burning zone opening from the bottom of said charging zone andcharacterized by moderately diverging Walls, y

(c) a gas deection zone opening from the bottom of said burning zone andcharacterized by sharply diverging walls, the degree of wall slope inthe gas stream deflection zone being on the order of about three timesas great as the degree of slope of the wall defining the burning zone,said gas stream deflection zone being located at about the midpoint ofthe vertical extent of the refractory lining in said shell,

{d) -a fuel injection zone opening from the bottom of said gasdeflection zone and characterized by moderately diverging walls, thedegree of slope of the wall which defines the fuel injection zone beingon the order of about one fourth the slope of the Wall which defines thegas stream deieetion zone, and

(e) a cooling zone of substantially uniform cross section openingfromvthe bottom of said fuel injection zone and terminating at the gasintake at the bottom of said kiln, the slopes typically being asfollows; about 11 from vertical in the burning zone, about 33 fromvertical in the gas deliection zone and about 7 from vertical in thefuel injection zone.

3. The shaft kiln of claim 1 in rwhich the charging zone extends for adistance approximately equal to 1/s to /l@ the vertical height of thekiln lining, the burning zone extends a subsequent distanceapproximately equal to the charging zone, the gas deection zone extendsfor a subsequent distance approximately equal to about 1/20 the verticalheight of the kiln lining, the fuel injection Zone extends for Iasubsequent distance approximately equal to about 3fm of the verticalheight of the kiln lining.

References Cited by the Examiner UNITED STATES PATENTS 1,447,071 2/1923Giescke 263-29 X FOREIGN PATENTS 938,178 1/1956 Germany.

FREDERICK L. MATTESON, In., Primary Examiner.

WILLIAM F. ODEA, Examiner.

A. D. HERRMANN, Assistant Examiner.

1. IN A VERTICAL, TUBULAR SHAFT KILN HAVING A BOTTOM GAS INTAKE AND ATOP GAS DISCHARGE, A TUBULAR OUTER SHELL, A REFRACTORY LINING POSITIONEDIN SAID SHELL, SAID REFRACTORY LINING CONSTRUCTED AND ARRANGED TO DEFINEAN INTERNAL PASSAGE, THE SLOPE OF THE INNER FACE OF THE LINING WHICHDEFINES THE INTERNAL PASSAGE PROGRESSIVELY DIVERGING AT SPACED POINTSFROM ADJACENT ITS TOP TO A POINT INTERMEDIATE ITS ENDS TO SEQUENTIALLYDEFINE CONTIGUOUS INTERCONNECTED TREATMENT ZONES IN THE FOLLOWINGPRECISE ORDER: (A) A CHARGING ZONE OF SUBSTANTIALLY UNIFORM CROSSSECTION EXTENDING FROM THE GAS DISCHARGE TO A POINT INTERMEDIATE THEENDS OF THE KILN, (B) A BURNING ZONE OPENING FROM THE BOTTOM OF SAIDCHARGING ZONE AND CHARACTERIZED BY MODERATELY DIVERGING WALLS, (C) A GASDEFLECTION ZONE OPENING FROM THE BOTTOM OF SAID BURNING ZONE ANDCHARACTERIZED BY SHARPLY DIVERGING WALLS, THE DEGREE OF WALL SLOPE INTHE GAS STREAM DEFLECTION ZONE BEING ON THE ORDER OF ABOUT THREE TIMESAS GREAT AS THE DEGREE OF SLOPE OF THE WALL DEFINING THE BURNING ZONE,SAID GAS STREAM DEFLECTION ZONE BEING LOCATED AT ABOUT THE MIDPOINT OFTHE VERTICAL EXTENT OF THE REFRACTORY LINING IN SAID SHELL, SAID GASDEFLECTION ZONE CAUSING THE PREHEATED AIR AND FUEL GASES TO BE DIVERTEDTOWARD THE CENTER OF THE INTERNAL PASSAGE, (D) A FUEL INJECTION OPENINGFROM THE BOTTOM OF SAID GAS DEFLECTION ZONE AND CHARACTERIZED BYMODERATELY DIVERGING WALLS, THE DEGREE OF SLOPE OF THE WALL WHICHDEFINES THE FUEL INJECTION ZONE BEING ON THE ORDER OF ABOUT ONE FOURTHTHE SLOPE OF THE WALL WHICH DEFINES THE GAS STREAM DEFLECTION ZONE, AND(E) A COOLING ZONE OF SUBSTANTIALLY UNIFORM CROSS SECTION OPENING FROMTHE BOTTOM OF SAID FUEL INJECTION ZONE AND TERMINATING AT THE GAS INTAKEAT THE BOTTOM OF SAID KILN.